1. Field of the Invention
The present invention relates to a method for warning a driver of a vehicle of a collision with an object, e.g., during parking.
2. Description of Related Art
Methods that warn a driver of a vehicle of a collision with an object during the process of parking are already known and commercially available. Such systems are usually referred to as parking assistants or parking aids. In such parking assistance systems, the distance of the vehicle to objects is recorded with the aid of distance sensors, which are positioned in the fender region of the vehicle as a rule. Via a visual and/or an acoustical display, the driver is informed about the distance to objects detected by the distance sensors. In this context it is common, for example, to provide LEDs for the visual display, the number of LEDs increasing with decreasing distance. At the same time, color coding is possible as well. For example, at a large distance the color of the LEDs is green, with decreasing distance it first turns yellow, and at a very small distance, to red. An acoustical display usually takes the form of successive signal tones, the amplitude between two tones decreasing with decreasing distance, and a continuous tone being transmitted if a minimum distance is undershot. At the same time, it is also possible for the tone frequency to vary with decreasing distance.
In addition to such parking assistance systems, which detect only the distance of the vehicle to objects and display it to the driver, there are also systems which support the driver when parking in a parking space. Such a parking assistance system either provides the driver with information about the required steering movements, or the system itself takes control of the steering operation. The driver's task consists only of accelerating the vehicle, maintaining the speed, or braking. In this case as well, the driver is informed about the distance to objects via distance sensors, so that the driver is able to bring the vehicle to a standstill in a timely manner before a collision occurs.
Especially when parking in perpendicular parking spaces, the parking operation is usually performed in several reverse and forward driving moves. If the vehicle is to be parked in the perpendicular parking space by backing into it, then a reverse move takes place to begin with. With this move, the vehicle is normally not pulled into the parking space directly, but instead is driven at an angle in reverse and closely approaches one of the objects delimiting the parking space; usually another vehicle. In the process, the rear of the vehicle to be parked comes close to the objects delimiting the side of the parking space. If the driver does not brake the vehicle in time, a cost-intensive collision of the fender of the vehicle to be parked with the side of an adjacent vehicle will result. In currently used systems for detecting the environment, such as the one described in US Patent Application Publication No. 2007/0091625, the output signals are fixedly set for certain distances. Thus, the driver receives a warning at always the same distance to an object, regardless of the situation in which the driver finds himself.
In particular when the costly collision in the course of perpendicular parking is looming, the warning by the parking assistance system may possibly arrive too late to prevent a collision. In a parking situation involving longitudinal parking, however, a brief and reliable warning is often desired.
For the output of a sufficiently timely warning, systems for automatically controlled parking are known to record the parking situation while driving past the parking space, by measuring it laterally with the aid of ultrasonic, radar or video sensors. The warning instant may therefore be output as a function of a calculated distance between the vehicle and an object, or as a function of the vehicle speed and the distance. The warning is output based on the collision instant, the so-called time-to-impact. However, the precision of the object positions in such a map of the environment measured while in passing may possibly be compromised, because the two-fold standard deviation is usually greater than 25 cm. Therefore, such methods are of limited use. In one alternative variant of such a time-to-impact warning, it is possible to implement the warning solely on the basis of currently acquired measured values and the current vehicle speed. In addition, it is also known to output such a warning when all of a sudden an object is detected which does not exist in the map of the environment and as a consequence most likely involves a moving object that the driver possibly has not seen either. Such a moving object is a pedestrian, for instance. However, these methods are only of limited advantage when maneuvering at slow speeds since a time-to-impact warning at slow speeds is likewise able to provide only a slight time delay in the warning.